A serving is the amount of food recommended in consumer education materials such as MyPlate. A portion is the amount of a food you choose to eat at any one time â which may be more or less than a serving. Here are some everyday comparisons to help you figure out your serving sizes. 1  1 teaspoon of margarine is the size of one dice. 2  3 ounces of meat is the size of a deck of cards. 3  1 cup of pasta is the size of a baseball. 4  1Â½ ounces of cheese is the size of four stacked dice.
1 If the oxygen concentration in the blood decreases, they tell the respiratory centers to increase the rate and depth of breathing.  Carbon dioxide: Peripheral chemoreceptors also monitor the carbon dioxide concentration in the blood.
The central chemoreceptors do not directly detect the arterial CO2 tension. Instead, they detect decreases in the CSF pH. These two values are connected because arterial CO2 diffuses past the blood brain barrier, into the CSF, and is converted by carbonic anhydrase to carbonic acid that in turn decreases the CSF pH.